Straight-line-motion mechanism



April 8, 1930. 'w. K. RANKIN 1,754,179

STRAIGHT LINE MOTION MECHANISM- Filed Aug. 4, 192'? I l PI InvenTor' William K.Rcmki-n, b3 M His Al'for'ne Patented Apr. 8, 1930 UNITED STATES PATENT OFFEOE WILLIAM K. RANKIN, OF SGOTIA, NEW YORK, ASSIG-NOR TO GENERAL ELECTRIC COM- PANY, .A. CORPORATION OF NEW YORK STRAIGHT-LINE-MOTION MEGI-IANISM Application filed August 4, 1927.

My invention relates to straight line motion mechanisms and particularly to mechanisms of this character applied to electric switches whereby the operating rod of the switch is moved approximately in a straight line. An object of my invention is the provision of an improved straight line motion mechanism which is simple, compact and economical in construction and eflicient in operation.

My invention will be better understood from the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims. 1

Referring to the drawing, Fig. 1 shows an electric switch operating mechanism involving my invention; and Fig. 2 is a diagrammatic representation of the mechanism.

With reference first to Fig. 2, the straight line motion mechanism which I have devised comprises essentially the member 1, the lever 2 and the link 3. Member 1 has the fixed pivot point 4 adjacent one end and adjacent the other end is pivoted to lever 2 at the central point 5 thereof. The point 6 at one end of lever 2 is the point which it is desired to have follow as closely as possible the straight vertical line 7. At the opposite end of lever 2 is the offset 8 at the end of which is the pivot point 9 where pivotal connection is made with the lower end of supporting link 3, the upper end of the link having a fixed pivot 10. Member 1 is shown materially longer than that part of lever 2 between points 5 and 6.

Straight line motion mechanisms heretofore commonly have been constructed on the general plan shown in Fig, 2 but with the lever 2 a simple straight member having the pivot 5 in the middle and the member 1 equal in length to the distance between the points 5 and 6. Where that end of the lever 2 0p posite the point 6 was guided to move in a straight horizontal line the point 6 moved in a straight vertical line. For simplicity and convenience the aforesaid end of lever 2 instead of being mounted in a straight guide has been pivoted to the end of a supporting link such as link 3. If the link were rela- Serial No. 210,705.

tively long so that the path described by the pivotal point thereof with the levcr'departed but slightly from a straight line the error introduced in the path taken by the point 6 was slight. In certain applications of straight line motion mechanisms, however, it is inconvenient by reason of space limitations or otherwise to use a link 3 having a length sutficient to prevent the point 6 from moving in a path which departs to an objectionable degree from the ideal straight line. One of many examples of such applications is the operating mechanism of an electric switch where it is desirable to have the operating rod of the switch move in an approximately straight line and yet have the mechanism simple and compact in form.

In certain applications also exemplified in electric switches it is desirable for structural reasons to arrange the fixed pivot point l of the member 1 at one side of the line of motion of the point 6, thus in the case of a switch structure avoiding interference between a shaft forming the pivot of member 1 and the vertically operated switch rod. With mechanisms as heretofore constructed, a necessary displacement of the pivot point 4 out of the line 7 for practical purposes resulted in causing the point 6 to deviate an objectionable amount from that line.

I have-found that the error introduced by the desired displacement of thepivot point 4: from the line 7 and the error introduced by the use of a supporting link 3 which is relatively short may be compensated to a large extent by arranging the points ,6, 5 and 9 of lever 2 displaced slightly from a straight line. For convenience in explaining my invention I have shown the lever 2 having an offset 8 to the end of which is pivoted the supporting link whose length is such that its stationary pivot point 10 is approximately only as high as the highest point normally reached by the point 6. I have shown by dot and dash lines the member 1 and lever 2 in various positions of their movement to illustrate how very closely the point 6 follows the straight line 7 It will be noted that the point of the elbow 12 of lever 2 traces a path for the greater portion of its movement which is a fiat curve closely approaching the horizontal straight line 13, much flatter in fact than the circular are 14 traced by the point 9, the offset 8 inclining more and more as the are 14 approaches the line 13.

In Fig. 1 I have shown an application to an electric switch of the mechanism shown diagrammatically in Fig. 2. In that figure the switch cover 16 is shown having a separate removable top cover 17 to which is pivoted the supporting link 18 corresponding to To the to. cover 17 is selink 3 of Fig. 2. cured the depending pivot supports 19 which carry the pivot shaft 20 for the member 21 which in the present application 'isa double lever pivoted adjacent one end of the central portion of lever 22 and pivotally connected at the opposite end to the actuating mechanism comprising the toggle links 23 and 24, shaft 25, crank 26 and actuating rod 27. The switch operating rod 28 which preferably should move in as nearly a straight line as is practicable is pivoted to the lever 22 and at all times is spaced with sufficient clearance from the pivot shaft 20. In the construction illustrated lever 22 has that end connected to the operating rod slightly curved whereby its intermediate pivot point is displaced the desired amount from the line joining the pivot points at its ends, it being immaterial to the operation of the mechanism what shape the lever takes so long as its three pivot points are displaced in the manner described and to the necessary extent.

By this construction I have provided a straight line motion mechanism which when applied to an electric switch of the enclosed mechanism type like that illustrated permits the use of a supporting link short enough to be conveniently enclosed by the mechanism housing and permits the spacing of the operating rod and the fixed pivot shaft of the actuating lever without causing the operating rod in its movement to depart from a straight line except to a negligible amount.

I have chosen the particular embodiment described above as illustrative of my invention and it will be apparent that various modifications may be made without departing from the spirit and scope of my invention which modifications I aim to cover by the appended claims.

WVhat I claim as new and desire to secure by Letters Patent of the United States, is

1. Straight line motion mechanism comprising a member having a fixed pivot point adjacent one end thereof, a lever pivoted centrally to the member adjacent the other end thereof, a link having a fixed pivot at one end and pivoted atits other end to one end of said lever, and an operated member attached to the other end of said lever, the central pivot point of the lever being ofiset from the line connecting the members attached at the opposite ends of the lever.

2. Straight line motion mechanism comprising a member having a fixed pivot point adjacent one end thereof, a lever pivoted centrally to the member adjacent the other end thereof, a link having a fixed pivot at one end and pivoted at its other end to one end of said lever, and an operated rod pivoted to the opposite end of said lever, the central pivot pointof said lever being offset from the line connecting the pivot points at the ends thereof in the direction of the fixed pivot.

3. Straight line motion mechanism comprising a member having a fixed pivot point adjacent one end thereof, a lever pivoted centrally to the member adjacent the other end thereof, a link having a fixed pivot point at one end and pivoted at its other end to one end of said lever, and an operating rod pivoted to the opposite end of said lever, the central pivot point of the lever being offset from the line oining the pivot points at the ends of the lever and the distance between. the pivot points of said member being materially greater than the distance between the central pivot point of the lever and the pivot point of the rod therewith.

4. Mechanism for moving a switch operating rod in a straight line in the direction of its length comprisinga first lever having an intermediate fixed pivot point, operating mechanism connected thereto, a second lever pivoted at one end to said operating rod and pivoted at a central point thereof to said. first lever, a link having a fixed pivot point at one end and pivoted at its other end to the other end of said second lever, said second leverhaving its pivot points lie on a curve convex toward, said link, the distance between the pivot points of said first lever being materially greater than the distance between the central pivot point of said second lever and the pivot point of the rod therewith and the fixed point of said link being approximately at the same height as the highest position taken by-the pivoted end of said operating rod.

In witness whereof, I have hereunto set my hand this 2nd day of August, 1927.

IVILLIAM K. RANKIN. 

